Command and Telemetry subsystems constitute two of the most important subsystems of the U.S. Air Force Space Lift Range System (SLRS) designed to provide operational support for the space launch vehicles. A command destruct signal (CDS) is sent to the launch vehicle (LV) if the trajectory of the LV poses any serious safety concerns. While the need to issue a CDS command is by necessity very infrequent, safety considerations require that this link have very high reliability under all conditions. It is also required to ensure that the command uplink can be closed with sufficient margin under the worst possible conditions and from any intended site(s). Under normal operating conditions when the only significant disturbance is the receiver thermal noise, there is no real concern in terms of providing such a margin as shown in some of the previous analyses. However, in the presence of the high power pulse interference, the performance can be very poor. As is intuitively obvious, when most of the period of the CDS pulse is interfered by the high power pulse, no detection takes place by the conventional FM receivers with analog or digital implementation.
The CDS command signal is comprised of a known sequence of pairs of pulsed tones in the received signal. The pairs of frequencies are selected from a predetermined set of seven tones. The CDS signal is sent to the launch vehicle, should the range safety considerations necessitate the vehicle's destruction. There is also a pilot tone that is transmitted independently and in addition to the sequence of pairs of pulsed tones. The traditional command receiver is comprised of an FM receiver for the demodulation of the pulsed tones and a command decoder that ascertains as to which tone pairs if any are present in the received signal during any pulse period and uses this information to finally determine whether or not a command signal is present in the received bandpass signal.
In the presence of high power pulse interference, the performance of the traditional command receiver is very poor in that there is virtually no detection possible with such a receiver. This is intuitively obvious and is also borne out by simulations. The performance can be partially improved by blanking; however, such an approach will work only under certain conditions and that too with a relatively large performance loss.